The present invention relates to a novel acetone complex of a sulfoxide compound or of a pharmacologically acceptable salt thereof useful as medicines such as inhibitors of gastric acid secretion and anti-ulcer agents or as intermediates for production of medicines, as described in JP-A 1-6270 (Example 32), JP-A 61-50978 (Example 2), JP-A 54-141783 (Example 21) or JP-A 61-22079 (Example 2), a process for producing the same and a purification method using the same.
Heretofore, sulfoxide compounds have been prepared by oxidizing thioether compounds with an oxidizing agent such as hydrogen peroxide, m-chloroperbonzoic acid, sodium hypochlorite, sodium hypobromite etc., as described in JP-A 1-6270 (EP 268956, U.S. Pat. No. 5,045,552), JP-A 61-50978 (EP 174726, U.S. Pat. No. 4,628,098), JP-A 54-141783 (EP 5129, U.S. Pat. No. 4,255,431), JP-A 61-22079 (EP 166287, U.S. Pat. No. 4,758,579) etc.
(See the following reaction scheme wherein R1 to R4 have the same meanings as defined below.) 
Among the oxidizing agents described above, m-chloroperbenzoic acid is frequently used from the viewpoint of easiness of weighing, storage stability, reaction activity etc.
For example, in Example 32 of JP-A 1-6270, thioether is oxidized with 0.96 equivalent (in terms of the amount of a purified product) of m-chloroperbenzoic acid, but in some cases, the reaction does not stop at the stage of sulfoxide, so there is the problem of the side reaction of further oxidation of a part of the formed sulfoxide into sulfone, as shown in the following reaction. As a matter of course, formation of the sulfone brings about the drawback of lower yield of the desired sulfoxide, and another problem is that it is difficult to separate and purify the 2 compounds because of their very similar physicochemical properties.
(In the following reaction, R1 to R4 have the same meanings as defined above.) 
Further, many sulfoxide compounds or their pharmacologically acceptable salt (III) are unstable to air, humidity, heat, light, pH etc., and their decomposition reaction occurs during purification procedures in conventional purification methods such as column chromatography etc., so there is the problem that the purity of their product can be lowered on the contrary. Further, during storage as raw material (bulk), they may also be partially decomposed to lower their purity, but no method for stable storage thereof for a prolonged period of time has been established.
Under the present circumstances as described above, there are no established methods for purifying and stabilizing industrially superior high-purity sulfoxide compounds or their pharmaceutically acceptable salts (III), so there is a need for new superior purification and stabilization methods.
The present inventors made extensive study to solve the problems described above. As a result, they have unexpectedly found the novel acetone complexes described below and that by using these complexes, the objective sulfoxide compounds or their pharmacologically acceptable salts (III) can be purified in high yield and high purity and further they can be stored as raw material (bulk) stably for a prolonged period of time, to arrive at completion of the present invention.
Accordingly, the present invention is to provide novel acetone complexes (I) of sulfoxide compounds or of their pharmacologically acceptable salts (III) useful as medicines such as inhibitors of gastric acid secretion and anti-ulcer agents or as intermediates for production of medicines, a purification method using the same and a method capable of storing sulfoxides or their pharmacologically acceptable salts (III) stably for a prolonged period of time.
Hereinafter, the present invention is described in detail.
First, the acetone complex (I) of a sulfoxide compound or of a pharmacologically acceptable salt thereof according to the present invention is represented by the following formula: 
wherein R1 represents a hydrogen atom, a methoxy group or a difluoromethoxy group, R2 represents a methyl group or a methoxy group, R3represents a 3 -methoxypropoxy group, a methoxy group or a 2,2,2-trifluoroethoxy group, and R4represents a hydrogen atom or a methyl group;
n represents an integer of 1 to 4, and
m represents an integer of 1 to 4,
whereupon n and m can vary within the above-described range, depending on reaction conditions such as treatment method, the amount of acetone used, solvent used in combination, treatment temperature, treatment time and stirring rate; and
B represents a hydrogen atom, an alkali metal atom or xc2xd alkaline earth metal atom.
In the above definition, the alkali atom includes e.g. sodium atom, potassium atom, lithium atom etc., and the alkaline earth metal atom includes e.g. calcium atom, magnesium atom etc., among which sodium atom or magnesium atom is more preferable.
The acetone complex (I) of a sulfoxide compound or of a pharmaceutically acceptable salt thereof includes e.g. acetone complex of Rabeprazole, Lansoprazole, Omeprazole or Pantoprazole, or acetone complexes of pharmaceutically acceptable salts thereof.
The acetone complex (I) of a sulfoxide compound or of a pharmaceutically acceptable salt thereof according to the present invention is a novel compound characterized by patterns or absorption peaks in powder X-ray analysis, NMR, IR etc. Further, the acetone complex (I) of a sulfoxide compound or of a pharmaceutically acceptable salt thereof has industrially very superior characters such as stability to conditions such as air, humidity, heat, light, pH etc., thus making the conventionally impossible long-term storage or long-distance transport of the raw material (bulk) possible.
For example, the 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole sodium salt acetone complex (II) according to the present invention is specifically characterized in that it has peaks at the following angles expressed in terms of 2xcex8, in a powder X-ray diffraction pattern (see FIG. 1), and/or peaks at wavelengths of 745.4, 803.1, 1010.2, 1093.0, 1268.1, 1298.5, 1381.4, 1465.2, 1584.5, 1710.6 and 2930.7 cmxe2x88x921 in an infrared absorption spectrum in potassium bromine (see FIG. 2), and/or peaks at xcex4 (ppm) 1.83-2.05 (m, 2H), 2.17 (s, 3H), 3.24 (s, 3H), 3.48 (t, J=6.2 Hz, 2H), 4.09 (t, J=6.2 Hz, 2H), 4.40 (dd, J=13.2 Hz, J=5.7, 1H), 4.72 (dd, J=13.2 Hz, J=5.7, 1H), 6.86 (m, 2H), 6.93 (d, J=5.7, 1H), 7.45 (m, 2H), and 8.27 (d, J=5.7 Hz, 1H) in a 1H-NMR (400 MHz, DMSO-d6) spectrum (see FIG. 3).
(1) Measurement Method
About 100 mg sample was measured for its powder X-ray diffraction pattern under the following measurement conditions.
(2) Measurement Conditions
Target: Cu
Filter: monochro
Voltage: 40 KV
Current: 20 mA
Slit: DS 1; RS 0.15, SS 1
Scan speed: 2 deg/min.
Range: 5-30
Measured in FT-IR in accordance with the Japanese Pharmacopoeia, general test methods, infrared absorption spectrum, and a potassium bromide tablet method.
Next, the sulfoxide compound of the present invention or its pharmacologically acceptable salt (III) is represented by the following formula: 
wherein R1, R2, R3, R4 and B have the same meanings as defined above.
The sulfoxide compound or its pharmacologically acceptable salt (III) is a known compound, and more specifically, mention can be made of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (general name: Rabeprazole free base) described in JP-A 1-6270 (Example 32), a compound (R1=H, R2=CH3, R3=H, R4=CH2CF3, n=1) (general name, Lansoprazole; chemical name, 2-{[4-(2,2,2-trifluoroethoxy)-3-methylpyridin-2-yl)methylsulfinyl}-1H-benzimidazole) described in JP-A 61-50978 (Example 2), 5-methoxy-2-[(4-methoxy-3,5-dimethyl-2-pyridyl)methylsulfinyl]-1H-benzimidazole (general name: Omeprazole) described in JP-A 54-141783 (Example 21), or 5-difluoromethoxy-2-[(4,5-dimethoxy-2-pyridyl)methylsulfinyl]-1H-benzimidazole (general name: Pantoprazole) described in JP-A 61-22079 etc., or pharmacologically acceptable salts thereof. Any of these compounds can be produced in methods described in the corresponding laid-open publications.
Hereinafter, the process of actually producing the acetone complex (I) of a sulfoxide compound or of a pharmacologically acceptable salt thereof according to the present invention is specifically described.
In the present invention, the acetone complex can be obtained basically by contacting the sulfoxide compound or its pharmacologically acceptable salt (III) with acetone or by dissolving it in acetone and subsequent crystallization thereof. Preferably, the sulfoxide compound or its pharmacologically acceptable salt (III) is dissolved in acetone, and the precipitated acetone complex is filtered and dried.
Further, other solvents may also be used in combination. For example, after the sulfoxide compound or its pharmacologically acceptable salt (III) is treated with acetone, at least one selected from the group consisting of lower hydrocarbons, lower ethers, cyclic ethers, acetonitrile and aromatic hydrocarbons can also be added thereto.
The sulfoxide compound or its pharmacologically acceptable salt (III) can also be treated with acetone in the presence of at least one selected form the group consisting of lower fatty acid esters, lower alcohols, ethers, cyclic ethers, acetonitrile, water, lower hydrocarbons and aromatic hydrocarbons.
Here, the lower hydrocarbons refer to linear or branched hydrocarbons having 5 to 8 carbon atoms, and specific examples include n-pentane, n-hexane, n-heptane, n-octane etc. The lower ethers refer to compounds having a linear or branched alkyl group having 1 to 6 carbon atoms bound symmetrically or unsymmetrically to an oxygen atom, and specific examples include ether, isopropyl ether etc. The cyclic ethers refer to compounds having 4 to 6 carbon atoms, and specific examples include tetrahydrofuran, tetrahydropyran, dioxane, dioxolane etc. The aromatic hydrocarbons refer to benzene compounds, and specific examples include benzene, toluene, xylene, decalin etc. The lower fatty acid esters refer to compounds having a fatty acid having 1 to 6 carbon atoms bound via an ester linkage to a linear or branched alcohol having 1 to 6 carbon atoms, and specific examples include methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate etc. The lower alcohols refer to linear or branched alcohols having 1 to 6 carbon atoms, and specific examples include methanol, ethanol, isopropanol, butanol etc.
Hereupon, the treatment temperature in the present invention is not limited, and the reaction can be conducted usually at an arbitrary temperature of xe2x88x9220xc2x0 C. to the boiling point, and good results are given even at room temperature.
The amount of the solvent used is not limited either, and usually, 0.1 to 10 ml acetone, preferably 0.25 to 7.5 ml, more preferably 0.5 to 5 ml is used per g of the sulfoxide compound or its pharmacologically acceptable salt (III) . When other solvents are used in combination, their amount and their combination are arbitrarily selected.
The treatment time is not limited either. It is usually 1 to 24 hours which may be varied depending on the treatment method (contacting or dissolution etc.), the amount of acetone used, the type and amount of other solvent used in combination, treatment temperature, stirring rate etc. The precipitated crystals are filtered and dried, whereby the objective acetone complex (I) of the sulfoxide compound or of its pharmacologically acceptable salt can be obtained.
The resulting acetone complex (I) of the sulfoxide compound or of its pharmacologically acceptable salt is converted into an aqueous solution and then lyophilized thereby giving the sulfoxide compound or its pharmacologically acceptable salt useful as medicine such as an inhibitor of gastric acid secretion and an anti-ulcer agent or as an intermediate for production of medicine.
Hereinafter, the present invention is described in more detail by reference to Examples and Reference Examples below, and it is needless to say that they are not intended to limit the present invention.